1. Field of the Invention
This invention relates to railroad car coupler systems and more particularly to draft gears for such systems where inserts are used in the draft gear to regulate frictional restraint as the draft gear acts to absorb and cushion impacting forces on the coupler system.
2. Prior art
Modern railroad car coupler systems typically include a draft gear to absorb and cushion impacting forces on the system and thus prevent structural damage to the system as well as the railroad car.
An early draft gear for a railroad car coupler system is set forth in U.S. Pat. No. 1,982,575. The gear includes a front and a rear follower to interact with a shank and a yoke of the coupler system respectively. The front follower is positioned to force a casing of the gear rearward wherein the rear follower acts to move a set of wedges. Movement of the wedges is frictionally impeded by wear plates as well as compression of a spring set. The wedges are held apart by leaf springs to compressively engage the wear plates.
A more modern draft gear is disclosed in U.S. Pat. No. 3,348,633. This gear includes a wedge which moves inward in response to an external force applied to the coupler system. The wedge interacts with a set of friction shoes located in a complementary set of friction shoe seats. Inward movement of the wedge and shoes is resisted by compression of elastomeric pads and friction between the shoes and friction shoe seats. Each friction shoe seat has a pair of grooves to hold a metallic lubricant to regulate the coefficient of friction between the shoe and seat. The metallic lubricant is disposed in the grooves from an insert which is first placed between a respective shoe and seat. A heavy duty hammer drop is then applied to the gear wedge to press the insert material into the grooves as well as outwardly between the shoe and friction shoe seat surfaces.